It is uncertain whether the lack of effectiveness of transfusion is because anaemia itself does not affect outcome or because the risks associated with current stored red cell transfusions out weigh physiological benefits

Pathophysiology of anaemia

Young adults can maintain oxygen supply at Hb of 40-50g/L by increasing cardiac output and oxygen extraction.

Heart and brain have high oxygen extraction ratios which limit these compensatory mechanisms.

Oxygen consumption is increased in the critically ill so anaemia may be less well tolerated.

A post hoc sub group analysis of the TRICC trial of patients with ischaemic heart disease showed a non-significant trend towards lower 30 day mortality in the liberal transfusion group. (Underpowered)

FOCUS study of elderly patients undergoing hip fracture surgery found no difference in mortality or cardiovascular complications between a liberal and restrictive transfusion strategy, despite 40% of patients having IHD.

TRACs study was similar in patients undergoing elective cardiac surgery and found no difference in mortality or severe morbidity.

Acute coronary syndrome

Anaemic patients developing acute coronary syndrome have worse outcomes and anaemia is more common as patients are older, widespread use of anti-platelets and blood loss during revascularisation procedures.